The present claimed invention relates to the field of electronic displays. More specifically, the present claimed invention relates to a spacer (e.g., support) structure for an electronic display, including flat panel displays.
In some displays including flat panel displays, a backplate is commonly separated from a faceplate using a spacer (e.g., support) structure. In high voltage applications, for example, the backplate and the faceplate are separated by spacer structures having a height of approximately 1-3 millimeters. For purposes of the present application, high voltage refers to an anode to cathode potential greater than 1 kilovolt. Illustratively, in flat panel displays, the backplate deploys an array of cathodes (e.g., electron emitters) and the faceplate deploys an array of pixels and serves as an accelerating anode for electrons emitted by the cathode array, which travel through high vacuum between the anode and the cathode. The space between the cathode array and the anodes is sealed by fusing frit, a mixture of powdered glass and various other agents that joins the backplate and the faceplate. The space is then evacuated.
Upon evacuation, atmospheric pressure exerts a force tending to collapse the faceplate into the backplate. The spacer structures are deployed to withstand this force and thus support the faceplate. In one embodiment, the spacer structure is comprised of several strips or individual wall structures each having a width of about 50 microns. The strips are arranged in parallel horizontal rows with each strip extending across the width of the flat panel display. The spacing of the rows of strips depends upon the strength and size of the backplate and the faceplate and the strips, their surface areas, and the concomitant force of atmospheric pressure. Because of this, it is desirable that the strips be extremely strong. The spacer structure must meet a number of intense physical requirements.
In a typical flat panel display, the spacer structure must comply with a long list of characteristics and properties. More specifically, the spacer structure must be strong enough to withstand the atmospheric forces which compress the backplate and faceplate towards each other. Additionally, each of the rows of strips in the spacer structure must be essentially equal in height, so that the rows of strips accurately fit between respective rows of pixels. Furthermore, each of the rows of strips in the spacer structure must be very flat to insure that the spacer structure provides uniform support across the interior surfaces of the backplate and the faceplate.
Spacer structures must also have good stability. More specifically, the spacer structure should not degrade severely when subjected to electron bombardment, high operating temperatures, temperature variations, and/or subjection to a vacuum. As yet another requirement, a spacer structure should not significantly contribute to contamination of the vacuum environment of the flat panel display. Spacer structures therefore should not significantly out-gas in vacuo at any point within its operational temperature and voltage ranges. Further, spacer structures should not be susceptible to contamination that may evolve within the evacuated space such that any of their required properties degrade.
Another requirement for a spacer structure for a display is that it cannot interfere with the trajectories of the electron beams emitted by the display""s cathode, for example a Spindt emitter array cathode, toward their target pixels on the faceplate, which functions electrically as an anode. Interfering with the electrons"" trajectories can cause image distortion, degradation, or failure. For these reasons, a spacer structure must not retain any significant electrostatic charge which could deflect the electrons"" trajectories by attraction or repulsion. Thus, the coefficient of emission of secondary electrons, e.g., the secondary electron coefficient of emission, must suffice such that, ideally, for every electron absorbed by the spacer structure, a numerically corresponding electron is emitted.
Special coatings may be applied to spacer structures to ensure a satisfactory secondary electron coefficient of emission. The energy of electrons impinging on different parts of the wall varies. Electrons impinging on the spacer structure near the cathode have an energy which is typically much less than the energy of electrons which strike the spacer structure near the anode. Thus, such coatings may be tailored such that the secondary electron coefficient of emission varies from one part of the spacer structure to another, e.g., the position of a part relative to the cathode and the anode. As a result of the variation in energy of impinging electrons, the secondary electron emission coefficient function of the wall will also vary significantly from the portion of the spacer structure near the cathode to the portion of the spacer structure near the anode.
Spacer structures should have a consistent and well-managed thermal coefficient of resistivity, such that its Ohmic resistance does not vary significantly with temperature, over the operating ranges of the display. In so far as the resistivity of the spacer structure does change with temperature, it is important that it varies uniformly and as little as possible. Further, spacer structures for displays should meet sheet resistance specifications. Further still, variations in wall resistance uniformity, especially in the resistance uniformity across the height of the wall, can cause a zero current shift, e.g., a variation in the electron beam along the wall due to improper electrical potential on the wall surface. Zero current shift variation causes image degradation due to visible distortion of a displayed image generated by the beam.
Excellent thermal conductivity is another important characteristic of a well-designed spacer structure. This ensures that the heat generated in the structures by the electron bombardment is transferred uniformly across the entire spacer structure. It also ensures that the temperature variation in a spacer structure is minimized significantly. Such variation could otherwise result in mechanical stresses and strains and/or structural changes, which can cause cracking, deformation, and failure. Such variation can also result in resistance changes.
Display cathodes and anodes can be somewhat intricate structures. For example, the cathode structure of a flat panel display can be an array of microscopic Spindt emitters and associated gates and other structures interconnected by a matrix of rows and columns of conductors. A corresponding anode can be an array of sub-pixels and a matrix of opaque material, such as what is sometimes called black chrome, placed proximately to the sub-pixels themselves to separate the regions between the sub-pixels. Since the support structures for such display are designed to resist the force of atmospheric pressure tending to collapse the faceplate towards the backplate, the ends of the support structures are in physical contact with the inner surfaces of both the faceplate and backplate. The support structures must therefore touch or be in close proximity to both the cathode and the anode. The support structures may or may not be buttressed in these areas, to prevent lateral movement. Buttressed or not, the support structures of such a flat panel display are mounted in focus waffles on their cathode-abutting end and in small indentations, such as in the black chrome on their anode-abutting end.
However, during the thermal cycling associated with the operation of the display, the support structures heat up during temperature rises with concomitant physical expansion and cool off during temperature drops with concomitant physical contraction. The degree to which the dimensions of the support structures change with thermal cycling is a function of its coefficient of thermal expansion (CTE), measured in units of meters per meter-degree Celsius. With reference illustratively to Prior Art FIG. 1, an anode faceplate 12 of a flat panel display 10 is supported by a wall type support structure 14. During the operational heatup of flat panel display 10, both glass faceplate 12 and wall 14 also rise in temperature and physically expand. As wall 14 heats up, it expands isotropically (e.g., vertically as well as horizontally) in both the positive and negative directions along the dimension X, e.g., in both the positive X and negative X direction. Conventionally, spacer structure materials have been formulated to minimize CTE mismatch between support and other display components, as well as to optimize the other physical properties discussed above. However, just so minimizing the spacer structures"" CTE mismatch can be problematic. It is appreciated that similar phenomena occur for cathode glass (e.g., backplates).
Where a mismatch exists between the CTE of glass faceplate 12 and the CTE of the wall 14, the wall 14 will expand at a different rate and to a different degree than faceplate 12. This can cause the wall 14 to rub and/or scrape against the materials such as black chrome and other matrix material, polyimide, and possibly pixel material of faceplate 12. Such scraping can have a number of deleterious effects on the operational performance of the display. For instance, debris can be sloughed off. This debris can contaminate the evacuated internal environment of the display, can degrade the vacuum, and can foul the cathode, which can cause scattering or absorption of emitted electrons, or otherwise interfere with their trajectories. Another effect of the scraping can be that actual pixel phosphors can be damaged, along with opaque pixel borders. In either event, the images that are to be displayed can be fouled or the operational performance of the display can otherwise be degraded.
Conventionally, these problems are addressed by determining the CTE of the material used to fabricate the spacer structures, composed to satisfy the litany of requirements described above. For example, one such material has a CTE on the order of 70-75xc3x9710xe2x88x927 per degree Celsius. Then an attempt is made to find glass material with a closely matching CTE for use as a faceplate and backplate (e.g., cathode glass) and a corresponding glass powder or frit for use as the sealing frame. Sometimes, exactly matching glasses are difficult to locate and glasses with CTEs approximating the CTE of the spacer structures are selected instead. Thus, another conventional technique has been to have glass custom-fabricated to match the CTE of the spacer structures. Both techniques require almost painstaking cooperation with other entities such as vendors, who are not directly involved in the fabrication of the displays. This relational reliance has proven problematic for a number of reasons.
It is appreciated that frit or sealing glass powder is usually derived from a composition different from that of the display glass. The CTE of the frit or sealing glass powder is matched both to the spacer material selected, as well as to the display glass. Commercially available frit materials are available, which approximate the CTE of display glass and spacer structures. Such frit materials typically have a high lead content.
The conventional approach of selecting glasses which approximate the CTE of the spacer structures yields varying, often sub-optimal results based on the closeness of the approximation. The conventional approach of having faceplate glasses custom-tailored to match the CTE of the spacer structures is expensive. Further, this approach is inefficient because a display fabricator becomes tied for this purpose to a very small pool of glass vendors, perhaps even a single glass supplier. The display fabricator is constrained by the availability of glass allocated by the small vendor pool, and the glass selected may not be the best material available. However, the limitations of the supplier pool may render it the sole selection, which can be sub-optimal. Glasses are readily available for applications such as displays, including flat panel displays. However, the CTE of some such glasses is on the order of 80-85xc3x9710xe2x88x927 per degree Celsius. Flat panel and other display glasses with CTEs in other ranges are also readily available.
In one conventional approach, glass-based ceramics have been proposed in an effort to alter thermal expansion. However, detrimental effects on strength and electrical properties of walls and other spacer structures composed therefrom limit the applicability of this approach to the fabrication of spacer structures. Alternatively, it is conceivable that a new fabrication technique for display support structures can be developed with significantly different materials. However, this would demand that the existing processes be substantially revamped, which would undoubtedly be costly and an inefficient use of presently available resources.
A need exists for a spacer structure for displays having a coefficient of thermal expansion (CTE) which matches or very closely approximates the CTE of a high quality, desirable glass from which other display structures such as faceplates and backplates (e.g., cathode glass) can be fabricated. A need also exists for a spacer structure for displays that is composed of a material that has a CTE that is tailorable within a range that closely matches the CTE range spanned by a variety of readily available high quality, desirable glass from which other display structures such as faceplates and backplates can be fabricated. A further need exists for a spacer structure for displays having a CTE that satisfies the foregoing while retaining all other properties characterizing requirements for use in displays. Further still, a need exists for a spacer structure, the CTE of which enables great flexibility in the selection of other display components, without having to revamp existing fabrication techniques. Yet further still, a need exists for a spacer structure that minimizes zero current shift.
A spacer structure (e.g., a support structure) for a display is disclosed that has a CTE which matches or very closely approximates the CTE of a high quality, desirable glass from which other display structures such as faceplates and backplates (e.g., cathode glass) can be fabricated. The spacer structure is composed of a material that has a CTE that is tailorable within a range that closely matches the CTE range spanned by a variety of readily available high quality, desirable glass from which other display structures such as faceplates and backplates can be fabricated. The spacer structure disclosed has a CTE that achieves the foregoing qualities and retains all other properties characterizing requirements for use in displays. Further, the spacer structure disclosed has a CTE that enables great flexibility in the selection of other display components, without having to revamp existing fabrication techniques. Further still, a spacer structure is disclosed that minimizes zero current shift.
In one embodiment, the materials from which spacer structures for displays are fabricated are combined in new formulations such that the CTE of the finished spacer structures fabricated therefrom is significantly higher than the CTE of conventional display spacer structures. In one embodiment, compounds are added to the materials from which spacer structures are fabricated such that the CTE of the finished spacer structures fabricated therefrom is significantly higher than the CTE of conventional display spacer structures. The spacer structures resulting from these embodiments meet or exceed the various other physical properties requirements for successful deployment and application under the intense electron bombardment in a high voltage field and high temperature exposure within the evacuated confines of an operational display, yet their CTE is significantly higher than that of conventional spacer structures.
In one embodiment, spacer structures are fabricated having a high CTE over a range of values from mixtures of zirconia (ZrO2) and alumina (Al2O3). In another embodiment, spacer structures are fabricated having a high CTE over a range of values from mixtures of magnesia (MgO) and alumina (Al2O3). In yet another embodiment, other compounds, such as titania (TiO2) and molybdenum trioxide (MoO3) and/or metallic molybdenum (Mo), are added to the mixtures mentioned above.
The CTE of spacer structures produced in one embodiment is on the order of 80-85xc3x9710xe2x88x927 per degree Celsius, which is advantageously in the range of readily available high quality display glasses. Utilization of such spacer structures fabricated from materials having a high CTE advantageously allows the selection of a wide variety of readily accessible glasses and other materials for the fabrication of other display components such as faceplates. This flexibility accords the further advantage of lowering fabrication costs for displays and greater material availability without having to revamp existing display fabrication techniques.
In yet still another embodiment, spacer structures are fabricated using mixtures containing ammonium octamolybdate ((NH4)4Mo8O26), instead of MoO3, which results in a more uniform distribution of molybdenum throughout the spacer structure. This more uniform molybdenum distribution achieves excellent resistance uniformity across the height of the wall. Advantageously, this resistance uniformity minimizes zero current shift.
These and other advantages of the present invention will no doubt become readily apparent to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the various drawing figures.